1. Field of the Invention
This invention relates generally to the field of Boring and Penetrating the Earth, and more particularly to method and apparatus for boring by fluid erosion.
2. Description of the Prior Art
The use of high pressure water jet streams for drilling and cutting of rock, coal and the like are well-known in the art and are exemplified by patents such as the following:
______________________________________ Juvkam-Wold 3,924,698 DRILL BIT AND METHOD OF DRILLING Hall et al. 3,927,723 APPARATUS FOR DRILLING HOLES UTILIZING PULSED JETS OF LIQUID CHARGE MATERIAL Morrison 1,661,672 APPARATUS FOR HYDRAULIC DRILLING Fehlmann 2,783,972 INSTALLATION FOR MAKING BORES IN A STRATUM Hayes 3,785,875 JET REAMER Acheson 3,576,222 HYDRAULIC JET DRILL BIT Noren 3,960,407 CUTTERS AND METHODS OF CUTTING ______________________________________
In each of the above patents a nozzle is generally attached directly to the supply pipe with little or no consideration given to whether the internal dimensions or contour of the supply pipe match that of the inlet section of the nozzle. This apparently is based on the general assumption that water is a perfect fluid without shearing stress and that according to Pascal's law the fluid pressure is transmitted equally in all directions. At lower pressures this is substantially true, however changes occur at extremely high pressures as involved herein of 10,000 p.s.i. to 25,000 p.s.i. In the dynamic situation encountered in water jet cutting, the water passes from a supply conduit where it travels at a low velocity, e.g., 50 ft. per second through an exit nozzle at a velocity greater than 1,000 ft. per second. In undergoing this extreme increase in velocity the fluid converges and accelerates toward the exit nozzle. Any projections or irregularities of surface within the fluid conduit near the exit nozzle is apt to cause disturbances and turbulence within the fluid stream before it exits from the nozzle. Such turbulence tends to disrupt the stability of the water jets as they exit from the nozzle. The jets are therefore more susceptible to premature breakup and their coherent lengths are greatly reduced. This reduces the effective cutting length and the maximum standoff distance that can be obtained with the nozzle.